More than 65% of inmates who showed aggressive behavior against others and/or themselves displayed severe aggression.

Researchers conducted a study in a large cohort of aggressive individuals who were recruited in a federal penitentiary in Montreal, Quebec, Canada in order to assess which clinical, behavioral, and biological characteristics can serve as predictors of severe aggressive behavior. Their findings were published in Progress in Neuro-Psychopharmacology & Biological Psychiatry.

The goal was to determine which psychiatric features, as well as biological and behavioral variables, differ between violent, aggressive inmates and non-aggressive inmates, and to identify whether the combination of psychopathological (antisocial behavior) and biological [peripheral levels of serotonin (5-HT), Tryptophan (Trp), and Kynurenine (Kyn)] markers differentiates aggressive and non-aggressive individuals.

During psychiatric evaluation, researchers assessed severe aggression against others by using the MacArthur Community Violence Instrument (MacCVI), and severe aggression against self was estimated by using the Lethality of Suicide Attempt Rating Scale (LSARS). They also assessed lifetime presence of mood disorders, anxiety disorders, psychosis, pathological gambling, substance abuse/dependence (SCID-I), and personality disorders (SCID-II).

Serum levels of Trp, 5-hydroxytryptophan (5-HTP), 5-HT, and Kyn were analyzed using a high performance liquid chromatography (HPLC) system. They also calculated the ratios of 5-HT/Trp and Kyn/Trp.

Descriptive data show that more than 65% of inmates who showed aggressive behavior against others and/or themselves displayed severe aggression. Severe aggression was operationalized as “the intent to seriously harm or kill others or themselves.”

With regard to clinical characteristics, present findings are in line with previous reports showing that the group of aggressive inmates displayed significantly higher rate of mood disorders, psychosis, and substance abuse/dependence, and had a higher prevalence of anxiety disorders, as well as conduct, borderline, and antisocial personality disorders (ASPD), when compared with the characteristics of non-aggressive group of inmates. More specifically, “Logistic regression analysis revealed that aggressive inmates were 2 times more likely to have a mood disorder and 3 times more likely to have a conduct or ASPD,” investigators wrote in their publication.

In terms of biological measures, the group of aggressive inmates showed lower serum levels of Trp and Kyn, but higher serum levels of 5-HT and higher 5-HT/Trp ratio. The Kyn/Trp ratio was positively correlated with the number of severe aggressive acts, but only when the sub-group of inmates who displayed severe aggression is taken into account.

With regard to behavioral characteristics, aggressive inmates displayed lower IQ and GAF, but higher levels of impulsivity and ADHD.

In order to establish the best predictors of aggressive behavior, researchers combined psychiatric, behavioral, and biological variables. By using logistic regression and ROC curve analysis, final data indicate, “That only a combination of ASPD, 5-HT/Trp ratio, and GAF-Axis V generates a good predictive power of aggressive behavior."

“Given the heterogeneous construct of aggress, only a combination of biological and psychopathological markers, namely high 5-HT/Trp ratio in the serum, presence of ASPD, and low GAF score, may better help predicting aggressive behavior,” investigators concluded.